1. Field of the Invention
This invention relates to an electronic camera having an electronic shutter function and capable of performing high-speed successive photographing operations.
2. Description of the Prior Art
Heretofore, most of electronic still-picture cameras for recording an image of an object on a magnetic sheet using a CCD and the like use mechanical shutters like cameras using silver-salt films. When performing successive photographing operations in such an electronic camera, there is generally used a sequence in which, after exposure has been performed by driving a shutter, a stepping motor or the like is driven for moving a head to the next track, and, after terminating the movement of the head, the shutter is recharged to prepare for the next photographing operation.
In the case of using such a mechanical shutter, however, its operation time is not constant due to differences in shutter mechanism between cameras, different power-supply voltages, ambient temperature, humidity and the like. Furthermore, the fact that the operation time itself is long is an obstacle in performing high-speed successive photographing operations and the like.
Taking into consideration the problems as described above, the use of an electronic shutter by means of electronic control of an imaging device, such as a CCD or the like, instead of a mechanical shutter is effective as means for increasing successive photographing speed.
In a conventional electronic camera, however, an electronic shutter pulse is output in accordance with a shutter release, and, after having thereby once cleared the electric charges stored in the CCD, exposure is performed. Recording is then performed, and the head is moved to the next track.
After the completion of the movement of the head, an electronic shutter pulse is output by catching the next vertical synchronizing signal V.sub.s, and subsequently the same operation is repeated.
The operation is illustrated in FIG. 7. That is, since the moving period of the head is not particularly considered for the electronic shutter operation, the timing of the V.sub.s signal has already passed when the movement of the head is completed. Hence, there is a waste of time such that it is necessary to wait for another V.sub.s in order to output the next electronic shutter pulse. This results in the disadvantage that the successive photographing speed does not become very high.